Cutting tool

ABSTRACT

The present invention provides a cutting tool in which the hard coating layer demonstrates superior chipping resistance. The cutting tool has a tool base composed with tungsten carbide-based cemented carbide or titanium carbonitride-based Cermet, and a hard coating layer provided on the surface thereof; wherein the hard coating layer includes: (a) a Ti compound and/or Zr compound layer, which is a lower layer, comprising one or more layers of a TiC layer, TiN layer, TiCN layer, TiCO layer, TiCNO layer, ZrC layer, ZrN layer, ZrCN layer, ZrCO layer, ZrCNO layer and (b) an aluminum oxide layer having an α crystal structure which is an upper layer, including the highest peak in the inclination section within a range of 0-10.

BACKGROUND OF THE INVENTION

1. Incorporation by Reference

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application Nos. 2003-053059 filed on Feb. 28, 2003 and2003-056639 filed on Mar. 4, 2003. The contents of the applications areincorporated herein by reference in their entirety.

2. Field of the Invention

The present invention relates to a Cermet cutting tool having a coatedsurface (to be referred to as a coated Cermet cutting tool) used forhigh-speed, intermittent cutting of various types of steel, cast ironand so forth, and its hard coating layer in particular demonstratessuperior chipping resistance.

3. Description of the Related Art

Known examples of coated Cermet cutting tools comprise a base (to begenerically referred to as the tool base) made of tungsten carbide(WC)-based cemented carbide or titanium carbide (TiC)-based Cermet, anda hard coating layer. This hard coating layer comprises:

-   (a) a Ti compound and/or Zr compound layer, which is a lower layer,    comprising one or more layers of a Ti carbide (TiC) layer, Ti    nitride (TiN) layer, Ti carbonitride (TiCN) layer, Ti oxicarbide    (TiCO) layer, Ti oxicarbonitride (TiCNO) layer, Zr carbide (ZrC)    layer, Zr nitride (ZrN) layer, Zr carbonitride (ZrCN) layer, Zr    oxicarbide (ZrCO) layer and Zr oxicarbonitride (ZrCNO) layer formed    by chemical vapor deposition (to be simply referred to as vapor    deposition formation), and having an overall mean layer thickness of    0.5-2.0 μm, and-   (b) an aluminum oxide layer having an α crystal structure in the    vapor deposited state (to be referred to as an α-Al₂O₃ layer), which    is an upper layer, and having a mean layer thickness of 1-30 μm.

These coated Cermet cutting tools are widely known to be used forcontinuous and intermittent cutting of various types of steel, cast ironand so forth.

In addition, Japanese Unexamined Patent Application, First PublicationNo. Hei 6-31503 discloses that the Ti compound layer and the α-Al₂O₃layer, which compose a hard coating layer, have a particulate crystalstructure.

Moreover, Japanese Unexamined Patent Application, First Publication No.Hei 6-8010 discloses a technology for improving the strength of a TiCNlayer comprising the Ti compound layer in which the TiCN layer is madeto contain a longitudinally growing crystal structure by vapordeposition with an ordinary chemical vapor deposition device in anintermediate temperature range of 700-950° C. using a mixed gascontaining organic carbonitride as the reactive gas.

Cutting devices have recently come to be required to offer higherperformance, and there are also strong needs for saving of labor, savingof energy and reduced costs with respect to cutting processing.Accompanying these needs, the speed of cutting processing is tending tobecome even faster, resulting in the unavoidable circumstances ofcutting processing under heavy-duty cutting conditions including greatercutting depth and faster feeding.

There are no problems with the use of the conventional coated Cermetcutting tools in the case of continuous or intermittent cutting of steelor cast iron and so forth under ordinary conditions. However, althoughthe α-Al₂O₃ layer that composes the hard coating layer has superior heatresistance, since it is not provided with adequate strength, when usedfor high-speed intermittent cutting under severe cutting conditions,namely high-speed intermittent cutting in which thermal shock isrepeatedly applied at an extremely short pitch to the cutting edge,chipping occurs easily in the hard coating layer. As a result, thecutting tool reaches the end of its service life in a comparativelyshort period of time.

SUMMARY OF THE INVENTION

Therefore, the inventors of the present invention conducted research toimprove chipping resistance by focusing on a Cermet cutting toolcomprising an α-Al₂O₃ layer as the hard coating layer. As a result, thefollowing research results were obtained.

-   (1) When an α-Al₂O₃ layer, which comprises a hard coating layer, is    formed on the surface of a cutting tool by vapor deposition, prior    to this formation by vapor deposition, an Al₂O₃ core (the Al₂O₃ core    is preferably an Al₂O₃ core thin film having a mean layer thickness    of 20-200 nm, to be referred to as an Al₂O₃ core thin film) is    formed on the surface of the Ti compound and/or Zr compound layer,    which is a lower layer, using an ordinary chemical vapor deposition    device under low-temperature conditions of a reactive gas    composition, in % by volume, of AlCl₃: 3-10%, CO₂: 0.5-3%, C₂H₄:    0.01-0.3% and H₂: remainder, reaction atmosphere temperature of    750-900° C., and reaction atmosphere pressure of 3-13 kPa.

Next, an α-Al₂O₃ layer is formed under ordinary conditions on the Al₂O₃core thin film which is heat treated under conditions in which thereaction atmosphere is changed to a hydrogen atmosphere at a pressure of3-13 kPa and the reaction atmosphere temperature is raised to 1100-1200°C. The α-Al₂O₃ layer obtained in this manner was confirmed todemonstrate a pole plot graph in which the highest peak of theinclination section appears within a narrow range.

Specifically, as shown in the sketch drawings in FIG. 1, the inclinationof the normal of the (0001) plane of crystal grains relative to thenormal of the surface polishing plane is measured by emitting anelectron beam onto individual α-Al₂O₃ crystal grains having a hexagonalcrystal lattice present within the measuring range of the surfacepolishing plane using a field emission scanning electron microscope.Next, the measured inclinations within the range of 0-45 degreesindicated by the individual crystal grains are divided for each pitch of0.25 degrees, and a pole plot graph is prepared in which the measuredinclination present in each section are tabulated for each section. Inthis case, as shown in FIG. 2, the pole plot graph is shown in which thehighest peak of the inclination division appears within a narrow rangeof 0-10 degrees.

Furthermore, as shown in FIG. 3, a conventional α-Al₂O₃ layer wasconfirmed to have a pole plot graph in which a gradual highest pitch ofthe inclination section appears over a wide range of 25-35 degrees.

-   (2) An α-Al₂O₃ layer formed by vapor deposition on the heat-treated    Al₂O₃ core thin film has significantly improved strength as compared    with a conventional α-Al₂O₃ layer. Thus, a coated Cermet cutting    tool in which a hard coating layer was formed by vapor deposition as    the upper layer was confirmed to demonstrate superior chipping    resistance as compared with a conventional Cermet cutting tool in    which a conventional α-Al₂O₃ layer was formed by vapor deposition.

The present invention is based on these research results. In order tosolve these problems, the present invention provides a cutting toolprovided with a tool base composed with WC-based cemented carbide orTiCN-based Cermet, and a hard coating layer; wherein the hard coatinglayer comprises:

-   (a) a Ti compound and/or Zr compound layer, which is a lower layer,    comprising one or more layers of a TiC layer, TiN layer, TiCN layer,    TiCO layer, TiCNO layer, ZrC layer, ZrN layer, ZrCN layer, ZrCO    layer and ZrCNO layer, which are formed by vapor deposition, and    having an overall mean layer thickness of 0.5-20 μm, and-   (b) an aluminum oxide layer having an α crystal structure in the    state of being formed by vapor deposition (α-Al₂O₃ layer), which is    an upper layer, comprising the highest peak in the inclination    section within a range of 0-10 degrees in the case of emitting an    electron beam onto individual crystal grains having a hexagonal    crystal lattice present within the measuring range of the surface    polishing plane, measuring the inclination of the normal of    the (0001) crystal plane of the crystal grains relative to the    normal of the surface polishing plane using a field emission    scanning electron microscope, dividing the measured inclinations    within a range of 0-45 degrees indicated by the individual crystal    grains for each pitch of 0.25 degrees, and preparing a pole plot    graph by tabulating the measured inclinations present in each    section for each section, and having a mean layer thickness in a    range of 1-30 μm.

In the cutting tool of the present invention, the α-Al₂O₃ layer, whichcomposes the hard coating layer, exhibits a pole plot graph in which thehighest peak appears in the inclination section within a range of 0-10degrees as shown in FIG. 2, and demonstrates superior chippingresistance. Thus, the cutting tool of the present invention exhibitssuperior wear resistance and cutting performance over a long period oftime even during high-speed intermittent cutting of various types ofsteel and cast iron that is accompanied by extremely high levels ofmechanical and thermal shock as well as the generation of a large amountof heat.

In the cutting tool, it is preferable for the hard coating layer to havean aluminum oxide core thin layer containing an aluminum oxide corebetween the lower layer and the upper layer.

In the cutting tool, it is preferable for the mean layer thickness ofthe aluminum oxide core thin layer to be in a range of 20-200 nm.

In the cutting tool, it is preferable that the hard coating layer isobtained by forming the Ti compound and/or Zr compound layer; formingthe aluminum oxide core thin layer on the surface of the Ti compoundand/or Zr compound layer under conditions of a reaction gas composition,in % by volume, of AlCl₃: 3-10%, CO₂: 0.5-3%, C₂H₄: 0.01-0.3% and H₂:remainder, a reaction atmosphere temperature of 750-900° C. and areaction atmosphere pressure of 3-13 kPa; and heating the aluminum oxidecore thin layer to 1100-1200° C. under conditions in which the reactionatmosphere is hydrogen and the reaction pressure is 3-13 kPa; andforming the aluminum oxide layer having an α crystal structure on theheated aluminum oxide core thin layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are sketch drawings showing the measuring range ofinclination of the normal of the (0001) plane of crystal grains in anα-Al₂O₃ layer which comprises a hard coating layer.

FIG. 2 is a pole plot graph of the (0001) plane of an α-Al₂O₃ layerwhich comprises a hard coating layer of the cutting tool of the presentinvention.

FIG. 3 is a pole plot graph of the (0001) plane of an α-Al₂O₃ layerwhich comprises a hard coating layer of a cutting tool of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

As was previously explained, the cutting tool of the present inventionis provided with a tool base composed with WC-based cemented carbide orTiCN-based Cermet, and a hard coating layer. The hard coating layerfurther comprises a Ti compound and/or Zr compound layer, which is alower layer, and an α-Al₂O₃ layer, which is an upper layer.

The reasons for limiting the mean layer thicknesses of the upper andlower layers of the hard coating layer in the manner previouslydescribed are as indicated below.

(a) Ti Compound and/or Zr Compound Layer

The Ti compound and/or Zr compound layer is basically present as thelower layer of the α-Al₂O₃ layer. Since it has superior strength, thehard coating layer comprising it also has superior strength. Inaddition, since it is securely adhered to both the tool base and theα-Al₂O₃ layer, it contributes to improved adhesion of the hard coatinglayer to the tool base. If the mean layer thickness is less than 0.5 μm,the actions are unable to be fully demonstrated. On the other hand, ifthe mean layer thickness exceeds 20 μm, the thermoplastic deformationoccurs easily during high-speed intermittent cutting accompanying thegeneration of high levels of heat, in particular, thereby causing unevenwear. Consequently, the mean layer thickness of the Ti compound and/orZr compound layer is defined to be 0.5-20 μm.

(b) α-Al₂O₃ Layer

The α-Al₂O₃ layer improves wear resistance of the hard coating layerbecause Al₂O₃ itself has high hardness and superior heat resistance. Atthe same time, since the α-Al₂O₃ layer of the present invention hassuperior strength as compared with conventional α-Al₂O₃ layers, it actsto further improve the chipping resistance of the hard coating layer.However, the effects are unable to be adequately demonstrated if itsmean layer thickness is less than 1 μm. On the other hand, if it isthicker than 30 μm, chipping occurs easily. Consequently, the mean layerthickness of the α-Al₂O₃ layer is defined to be 1 30 μm.

(c) Heat-Treated Al₂O₃ Core Thin Film

There is a close relationship between the inclination section indicatingthe highest peak and the ratio of the heat-treated Al₂O₃ core thin film,in a pole plot graph of the α-Al₂O₃ layer. If the ratio of theheat-treated Al₂O₃ core thin film is too low, it becomes difficult toadjust the inclination section where the highest peak appears to withinthe range of 0-10 degrees, and it also becomes difficult to impart asatisfactory level of strength to the α-Al₂O₃ layer formed by vapordeposition thereon. Consequently, the effect of improving chippingresistance is unavoidably inadequate. Thus, it is preferable to providean Al₂O₃ core thin film, and particularly a heat-treated Al₂O₃ core thinfilm. Its mean layer thickness is preferably 20 nm or more, and morepreferably 30 nm or more. On the other hand, since it becomes difficultto make the inclination section where the highest peak appears to bewithin the range of 0-10 degrees if its ratio becomes excessively large.Therefore, its mean layer thickness is preferably 200 nm or less, andmore preferably 150 nm or less.

Thus, the mean layer thickness of the Al₂O₃ core thin film formed on theTi compound and/or Zr compound layer prior to formation by vapordeposition of the α-Al₂O₃ layer is preferably 20-200 nm, and morepreferably 30-150 nm.

A TiN layer having a gold color tone may also be formed by vapordeposition as necessary as the uppermost surface layer of the hardcoating layer for the purpose of discriminating before and after use ofthe coated Cermet cutting tool. In this case, the mean layer thicknessof the TiN layer having a gold color tone is preferably 0.1-1 μm. If themean layer thickness is less than 0.1 μm, adequate discriminationeffects are unable to be obtained. In addition, a mean layer thicknessof up to 1 μm is adequate for the TiN layer to demonstrate adiscrimination effect.

EXAMPLES

The following provides a more detailed explanation of the cutting toolof the present invention by referring to Examples and ComparativeExamples.

As raw material powders, WC powder, TiC powder, ZrC powder, VC powder,TaC powder, NbC powder, Cr₃C₂ powder, TiN powder, TaN powder and Copowder having a mean particle diameter of 1-3 μm were prepared. Theseraw material powders were blended to the blending compositions shown inTable 1, wax was added to them, and they were then mixed using a ballmill for 24 hours in acetone. After drying under reduced pressure, thedried mixtures were pressed formed into green compacts of apredetermined shape at a pressure of 98 MPa. Next, the green compactswere vacuum sintered for 1 hour in a vacuum at 5 Pa at a predeterminedtemperature within the range of 1370-1470° C. After sintering, thecutting edges were subjected to honing of R=0.07 mm to produce toolbases A through F made of WC-based cemented carbide having the indexableinsert shape defined in ISO-CNMG 120408.

TABLE 1 Blending Composition (% by mass) Type Co TiC ZrC VC TaC NbCCr₃C₂ TiN TaN WC Tool A 7 — — — — — — — — Rem. Base B 5.7 — — — 1.5 0.5— — — Rem. C 5.7 — — — — — 1   — — Rem. D 8.5 — 0.5 — — — 0.5 — — Rem. E12.5 2 — — — — — 1 2 Rem. F 14 — — 0.2 — — 0.8 — — Rem.

In addition, as raw material powders, TiCN (mass ratio of TiC/TiN=50/50)powder, Mo₂C powder, ZrC powder, NbC powder, TaC powder, WC powder, Copowder and Ni powder having a mean particle diameter of 0.5-2 μm wereprepared. These powders were mixed to the blending compositions shown inTable 2, they were then wet-mixed for 24 hours with a ball mill. Afterdrying, they were press formed into green compacts at a pressure of 98MPa. Next, the green compacts were sintered for 1 hour at a nitrogenatmosphere at 1.3 kPa, at a temperature of 1540° C. After sintering, thecutting edges were subjected to honing of R=0.07 mm to produce toolbases a through f made of TiCN-based Cermet having the insert shape ofISO standard CNMG 120412.

TABLE 2 Blending Composition (% by mass) Type Co Ni ZrC TaC NbC Mo₂C WCTiCN Tool a 13 5 — 10 — 10 16 Rem. Base b 8 7 — 5 — 7.5 — Rem. c 5 — — —— 6 10 Rem. d 10 5 — 11 2 — — Rem. e 9 4 1 8 — 10 10 Rem. f 12 5.5 — 10— 9.5 14.5 Rem.

The Ti compound and/or Zr compound layers having the target layerthicknesses shown in Table 4 were first formed by vapor deposition asthe lower layer of the hard coating layer under the conditions shown inTable 3 (the 1-TiCN in Table 3 indicates the formation conditions of aTiCN layer having a longitudinally growing crystal structure describedin Japanese Unexamined Patent Application, First Publication No. Hei6-8010, while others indicate the formation conditions of an ordinaryparticulate crystal structure) using an ordinary chemical vapordeposition device on the surfaces of these tool bases A through F and athrough f.

TABLE 3 Formation Conditions Layers of Hard Coating Layer ReactionAtmosphere (numbers indicate Reaction Gas Composition PressureTemperature atomic ratios) (% by volume) (kPa) (° C.) TiC TiCl₄: 4.2%,CH₄: 8.5%, 7 1020 H₂: rem. TiN (first layer) TiCl₄: 4.2%, N₂: 30%, 30900 H₂: rem. TiN (other layer) TiCl₄: 4.2%, N₂: 35%, 50 1040 H₂: rem.1-TiC_(0.5)N_(0.5) TiCl₄: 4.2%, N₂: 20%, 7 1000 CH₃CN: 0.6%, H₂: rem.TiC_(0.5)N_(0.5) TiCl₄: 4.2%, N₂: 20%, 12 1020 CH₄: 4%, H₂: rem.TiC_(0.5)O_(0.5) TiCl₄: 4.2%, CO: 4%, 7 1020 H₂: rem.TiC_(0.3)N_(0.3)O_(0.4) TiCl₄: 4.2%, CO: 3%, 20 1020 CH₄: 3%, N₂: 20%,H₂: rem. ZrC ZrCl₄: 4.2%, CH₄: 8.5%, 7 1040 H₂: rem. ZrN ZrCl₄: 4.2%,N₂: 30%, 30 960 H₂: rem. ZrC_(0.5)N_(0.5) ZrCl₄: 4.2%, N₂: 20%, 7 960CH₃CN: 0.8%, H₂: rem. ZrC_(0.5)O_(0.5) ZrCl₄: 4.2%, CO: 4%, 7 1040 H₂:rem. ZrC_(0.3)N_(0.3)O_(0.4) ZrCl₄: 4.2%, CO: 3%, 20 1040 CH₄: 3%, N₂:20%, H₂: rem. α-Al₂O₃ AlCl₃: 2.2%, CO₂: 5.5%, 7 1000 HCl: 2.2%, H₂S:0.2%, H₂: rem.

TABLE 4-1 Tool Hard Coating Layer (parentheses: target layer thickness:μm unless indicated in nm) base 1st 2nd 3rd 4th 5th 6th 7th Type symbollayer layer layer layer layer layer layer Coated 1 A TiN 1-TiCN TiNTiCNO Al₂O₃ core thin film α-Al₂O₃ — Cermet (1) (17.5) (1) (0.5) (50 nm)(3) Cutting 2 B TiN 1-TiCN TiC TiCNO Al₂O₃ core thin film α-Al₂O₃ TiNTool of (1) (4) (4) (1) (80 nm) (8) (0.3) Examples 3 C TiN 1-TiCN TiCNOAl₂O₃ core thin film α-Al₂O₃ — — (1) (4.5) (0.5) (50 nm) (15) 4 D TiN1-TiCN TiC TiCNO Al₂O₃ core thin film α-Al₂O₃ — (0.5) (10) (2) (0.3)(100 nm) (3) 5 D TiC 1-TiCN TiCNO Al₂O₃ core thin film α-Al₂O₃ — — (1)(4) (1) (20 nm) (15) 6 E TiC 1-TiCN TiCO Al₂O₃ core thin film α-Al₂O₃ —— (0.5) 9 (0.5) (50 nm) (8) 7 F TiN TiC 1-TiCN Al₂O₃ core thin filmα-Al₂O₃ TiN — (1) (1) (8) (150 nm) (5) (0.1) 8 a TiCN 1-TiCN TiCO Al₂O₃core thin film α-Al₂O₃ — — (1) (8.5) (0.5) (200 nm) (10) 9 b TiC 1-TiCNAl₂O₃ core thin film α-Al₂O₃ TiN — — (1) (9) (100 nm) (5) (1) 10 c TiN1-TiCN TiC TiCNO Al₂O₃ core thin film α-Al₂O₃ — (0.5) (1.5) (0.5) (0.5)(80 nm) (20) 11 d TiN TiCN Al₂O₃ core thin film α-Al₂O₃ — — — (1) (19)(100 nm) (1) 12 e TiN TiC TiCN TiCO Al₂O₃ core thin film α-Al₂O₃ TiN (1)(1) (7) (1) (30 nm) (10) (0.1) 13 f TiCN TiC TiCNO Al₂O₃ core thin filmα-Al₂O₃ TiN — (0.5) (2) (0.5) (80 nm) (30) (0.3)

TABLE 4-2 Tool Hard Coating Layer (parentheses: target layer thickness:μm unless indicated in nm) base 1st 2nd 3rd 4th 5th 6th 7th Type symbollayer layer layer layer layer layer layer Coated 14 A ZrN ZrCN ZrN ZrCOAl₂O₃ core thin film α-Al₂O₃ — Cermet (1) (7.5) (1) (0.5) (50 nm) (6)Cutting 15 B ZrN ZrCN ZrC ZrCNO Al₂O₃ core thin film α-Al₂O₃ TiN Tool of(1) (4) (4) (1) (80 nm) (8) (0.3) Examples 16 C ZrN ZrCN ZrCNO Al₂O₃core thin film α-Al₂O₃ — — (1) (16.5) (0.5) (200 nm) (3) 17 D TiN 1-TiCNZrC ZrCNO Al₂O₃ core thin film α-Al₂O₃ — (0.5) (6) (2) (0.3) (100 nm)(12) 18 d ZrC ZrCN TiCNO Al₂O₃ core thin film α-Al₂O₃ — — (1) (2) (0.5)(20 nm) (20) 19 e ZrC ZrCN ZrCO Al₂O₃ core thin film α-Al₂O₃ — — (0.5)(9) (0.5) (50 nm) (10) 20 f ZrN ZrCO ZrCN Al₂O₃ core thin film α-Al₂O₃TiN — (1) (1) (8) (150 nm) (15) (0.1)

Next, Al₂O₃ core thin films of the target layer thicknesses shown inTable 4 were formed under low-temperature conditions in which a reactiongas composition comprising, in % by volume, AlCl₃: 6.5%, CO₂: 1.6%,C₂H₄: 0.13%, and H₂: reminder; a reaction atmosphere temperature: 820°C.; a reaction atmosphere pressure: 8 kPa; and a reaction time: 5-80minutes (the relationship between the layer thickness of the Al₂O₃ corethin film and a reaction time was assessed in advance by an experiment,similar to the case of the Ti compound layer). Next, the Al₂O₃ core thinfilm was heat treated under conditions of changing the reactionatmosphere pressure to a hydrogen atmosphere at 8 kPa and raising thereaction atmosphere temperature to 1135° C. Subsequently, cutting toolsof Examples 1, 3-6 and 8-11, 14, 16-19 were produced by forming by vapordeposition the α-Al₂O₃ layers of the target layer thicknesses shown inTable 4 for the upper layer of the hard coating layer under theconditions shown in the Table 3.

Moreover, cutting tools of Examples 2, 7, 12, 13, 15 and 20 wereproduced by forming by vapor deposition the TiN layers of the targetlayer thicknesses shown in Table 4 for the uppermost surface layer ofthe hard coating layer under the conditions shown in the Table 3 on theresulting α-Al₂O₃ layers.

In addition, for the sake of comparison, comparative cutting tools 1through 20 were respectively produced under the same conditions with theexception of not forming the Al₂O₃ core thin film and not performingheat treatment prior to forming the α-Al₂O₃ layer of the hard coatinglayer as shown in Table 5.

TABLE 5 Hard Coating Layer (parentheses: target Tool layer thickness:μm) Base 1st 2nd 3rd 4th 5^(th) 6^(th) Symbol layer layer layer layerlayer layer Coated 1 A TiN 1-TiCN TiN TiCNO α-Al₂O₃ — Cermet (1) (17.5)(1) (0.5) (3) Cutting 2 B TiN 1-TiCN TiC TiCNO α-Al₂O₃ TiN Tools of (1)(4) (4) (1) (8) (0.3) Compara- 3 C TiN 1-TiCN TiCNO α-Al₂O₃ — — tive (1)(4.5) (0.5) (15) Examples 4 D TiN 1-TiCN TiC TiCNO α-Al₂O₃ — (0.5) (10)(2) (0.3) (3) 5 D TiC 1-TiCN TiCNO α-Al₂O₃ — — (1) (4) (1) (15) 6 E TiC1-TiCN TiCO α-Al₂O₃ — — (0.5) 9 (0.5) (8) 7 F TiN TiC 1-TiCN α-Al₂O₃ TiN— (1) (1) (8) (5) (0.1) 8 a TiCN 1-TiCN TiCO α-Al₂O₃ — — (1) (8.5) (0.5)(10) 9 b TiC 1-TiCN α-Al₂O₃ TiN — — (1) (9) (5) (1) 10 c TiN 1-TiCN TiCTiCNO α-Al₂O₃ — (0.5) (1.5) (0.5) (0.5) (20) 11 d TiN TiCN α-Al₂O₃ — — —(1) (19) (1) 12 e TiN TiC TiCN TiCO α-Al₂O₃ TiN (1) (1) (7) (1) (10)(0.1) 13 f TiCN TiC TiCNO α-Al₂O₃ TiN — (0.5) (2) (0.5) (10) (0.3) 14 AZrN ZrCN ZrN ZrCO α-Al₂O₃ — (1) (7.5) (1) (0.5) (6) 15 B ZrN ZrCN ZrCZrCNO α-Al₂O₃ TiN (1) (4) (4) (1) (8) (0.3) 16 C ZrN ZrCN ZrCNO α-Al₂O₃— — (1) (16.5) (0.5) (3) 17 D TiN 1-TiCN ZrC ZrCNO α-Al₂O₃ — (0.5) (6)(2) (0.3) (12) 18 d ZrC ZrCN TiCNO α-Al₂O₃ — — (0.5) (2) (0.5) (20) 19 eZrC ZrCN ZrCO α-Al₂O₃ — — (0.5) (9) (0.5) (10) 20 f ZrN ZrCO ZrCNα-Al₂O₃ TiN — (1) (1) (8) (15) (0.1)Production of Pole Plot Graphs

Pole plot graphs were respectively produced using a field emissionscanning electron microscope for the α-Al₂O₃ layers that compose thehard coating layer with the resulting coated Cermet cutting tools ofExamples 1-20 and coated Cermet cutting tools of Comparative Examples1-20.

Namely, the surface of the α-Al₂O₃ layer was placed inside the barrel ofa field emission scanning electron microscope as the polishing plane.Next, an electron beam having an acceleration voltage of 15 kV wasemitted onto individual crystal grains having a hexagonal crystallattice present within the measuring range of the surface polishingplane at an emission current of 1 nA and incident angle of 70 degreesrelative to the polishing plane. Inclination of the (0001) plane, whichis the crystal plane of the crystal grains, was measured relative to thenormal of the surface polishing plane in intervals of 0.1 μm/step for aregion measuring 30×50 μm using an electron backscattering diffractionimaging device. The measured inclination within the range of 0-45degrees indicated by each crystal grain was divided for each pitch of0.25 degrees based on the measurement results, and the measuredinclinations present in each section were tabulated for each section toprepare pole plot graphs.

The inclination sections in which the (0001) plane exhibits the highestpeak are respectively shown in Tables 6-1 and 6-2 in the resulting poleplot graphs of the α-Al₂O₃ layer.

TABLE 6-1 Inclination section in which Amount of flank (0001) plane ofα-Al₂O₃ layer wear (mm) indicates highest peak Alloy Carbon Cast(degrees) steel steel iron Coated 1 3.25-3.50 0.31 0.30 0.33 Cermet 21.00-1.25 0.23 0.24 0.25 Cutting 3 1.50-1.75 0.26 0.25 0.24 Tool of 42.75-3.00 0.32 0.31 0.34 Examples 5 8.00-8.25 0.38 0.36 0.35 6 2.00-2.250.28 0.28 0.29 7 5.25-5.50 0.33 0.34 0.37 8  9.75-10.00 0.37 0.36 0.36 92.25-2.50 0.29 0.29 0.31 10 0.50-0.75 0.23 0.21 0.21 11 3.50-3.75 0.380.39 0.45 12 4.25-4.50 0.34 0.33 0.33 13 0.00-0.25 0.25 0.20 0.19 143.00-3.25 0.30 0.32 0.31 15 1.50-1.75 0.24 0.25 0.26 16 1.00-1.25 0.260.24 0.26 17 2.75-3.00 0.32 0.30 0.33 18 8.50-8.75 0.39 0.38 0.36 191.50-1.75 0.25 0.26 0.27 20 5.00-5.25 0.34 0.32 0.35

TABLE 6-2 Inclination section in Cutting test results which (0001) planeof (time to reach service life) α-Al₂O₃ layer indicates Alloy CarbonCast highest peak (degrees) steel steel iron Coated 1 25.75-26.00 2.8min. 2.7 min. 2.9 min. Cermet 2 29.50-29.75 1.7 min. 1.5 min. 1.0 min.Cutting 3 33.50-33.75 0.5 min. 0.3 min. 0.3 min. Tools of 4 26.50-26.752.7 min. 2.9 min. 3.0 min. Comparative 5 32.25-32.50 0.5 min. 0.4 min.0.5 min. Examples 6 29.50-29.75 1.5 min. 1.8 min. 1.9 min. 7 27.50-27.752.0 min. 2.1 min. 1.6 min. 8 31.00-31.25 0.9 min. 0.7 min. 0.6 min. 926.25-26.50 2.2 min. 1.9 min. 1.9 min. 10 33.25-33.50 0.3 min. 0.3 min.0.5 min. 11 25.00-25.25 3.1 min. 2.6 min. 1.5 min. 12 31.50-31.75 1.1min. 0.8 min. 0.8 min. 13 34.75-35.00 0.2 min. 0.3 min. 0.5 min. 1425.75-26.00 2.9 min. 2.8 min. 2.7 min. 15 29.00-29.25 1.8 min. 1.7 min.1.2 min. 16 32.50-32.75 0.8 min. 0.5 min. 0.9 min. 17 28.50-28.75 2.5min. 2.8 min. 3.0 min. 18 34.25-34.50 0.5 min. 0.3 min. 0.7 min. 1929.25-29.50 1.7 min. 1.8 min. 2.0 min. 20 27.75-28.00 2.2 min. 1.9 min.1.8 min.Thickness of Each Layer of Hard Coating Layer

The thickness of each layer of the hard coating layers of the resultingcoated Cermet cutting tools of Examples 1-20 and Comparative Examples1-20 was measured using a scanning electron microscope (measurement oflongitudinal cross-section). As a result, all of the mean layerthicknesses (average of five measuring points) were confirmed to besubstantially the same as the target layer thickness. Furthermore,measurement of the layer thickness of the heat-treated Al₂O₃ core thinfilm in the coated Cermet cutting tools of Examples 1-20 was extremelydifficult.

Next, coated Cermet cutting tools of Examples 1-7 and 14-17 and coatedCermet coating tools of Comparative Examples 1-7 and 14-17 were boltedonto the end of a tool steel cutting bit followed by performing thecutting tests described below.

Dry High-Speed Intermittent Cutting Test Using Alloy Steel

The amount of flank wear of the cutting edge, or when that was unable tobe measured, the service life of the cutting edge, namely the amount oftime until chipping occurred in the hard coating layer, was measured.The cut material and test conditions used are indicated below. The testresults are shown in Table 6.

Cut material: Round bar composed of JIS-SCM440 in which fourlongitudinal grooves are formed at equal intervals in the direction oflength

Cutting speed: 350 m/min (normal cutting speed: 250 m/min)

Cutting depth: 1 mm

Feed: 0.25 mm/rev.

Cutting time: 5 min.

Dry High-Speed Intermittent Cutting Test Using Carbon Steel

Similar to the Dry High-Speed Intermittent Cutting Test Using AlloySteel, the amount of wear of the flank of the cutting edge or theservice life of the cutting edge was measured. The cut material and testconditions used are indicated below. The results are shown in Table 6.

Cut material: Round bar composed of JIS-S45C in which four longitudinalgrooves are formed at equal intervals in the direction of length

Cutting speed: 400 m/min (normal cutting speed: 300 m/min)

Cutting depth: 1 mm

Feed: 0.25 mm/rev.

Cutting time: 5 min.

Dry High-Speed Intermittent Cutting Test Using Cast Iron

Similar to these tests, the amount of wear of the flank of the cuttingedge or the service life of the cutting edge was measured. The cutmaterial and test conditions used are indicated below. The results areshown in Table 6.

Cut material: Round bar composed of JIS-FC300 in which four longitudinalgrooves are formed at equal intervals in the direction of length

Cutting speed: 450 m/min (normal cutting speed: 300 m/min)

Cutting depth: 1.5 mm

Feed: 0.25 mm/rev.

Cutting time: 5 min.

Moreover, the coated Cermet cutting tools of Examples 8-13 and 18-20 andthe coated Cermet cutting tools of Comparative Examples 8-13 and 18-20were bolted to the end of the tool steel cutting bit followed byperforming the cutting tests described below.

Dry High-Speed Intermittent Cutting Test Using Alloy Steel

Similar to these tests, the amount of wear of the flank of the cuttingedge or the service life of the cutting edge was measured. The cutmaterial and test conditions used are indicated below. The results areshown in Table 6.

Cut material: Round bar composed of JIS-SCM440 in which fourlongitudinal grooves are formed at equal intervals in the direction oflength

Cutting speed: 400 m/min (normal cutting speed: 250 m/min)

Cutting depth: 0.7 mm

Feed: 0.15 mm/rev.

Cutting time: 5 min.

Dry High-Speed Intermittent Cutting Test Using Carbon Steel

Similar to these tests, the amount of wear of the flank of the cuttingedge or the service life of the cutting edge was measured. The cutmaterial and test conditions used are indicated below. The results areshown in Table 6.

Cut material: Round bar composed of JIS-S45C in which four longitudinalgrooves are formed at equal intervals in the direction of length

Cutting speed: 400 m/min (normal cutting speed: 300 m/min)

Cutting depth: 0.7 mm

Feed: 0.15 mm/rev.

Cutting time: 5 min.

Dry High-Speed Intermittent Cutting Test Using Cast Iron

Similar to these tests, the amount of wear of the flank of the cuttingedge or the service life of the cutting edge was measured. The cutmaterial and test conditions used are indicated below. The results areshown in Table 6.

Cut material: Round bar composed of JIS-FC300 in which four longitudinalgrooves are formed at equal intervals in the direction of length

Cutting speed: 450 m/min (normal cutting speed: 300 m/min)

Cutting depth: 0.7 mm

Feed: 0.15 mm/rev.

Cutting time: 5 min.

As shown in Tables 4 through 6, in the coated Cermet cutting tools ofthe Examples 1-20, the (0001) plane of the α-Al₂O₃ layer indicated thehighest peak in the inclination section within the range of 0-10 degreesin the pole plot graphs. Consequently, these cutting tools demonstratedextremely high resistance to mechanical and thermal shock, and superiorchipping resistance even during high-speed intermittent cutting of steelor cast iron accompanied by the generation of a large amount of heat.The cutting tools significantly suppressed the occurrence of chipping ofthe cutting edge, and exhibited superior wear resistance.

In contrast, in the case of the Cermet cutting tools of ComparativeExamples 1 to 20, the (0001) plane of the α-Al₂O₃ layer, which is theupper layer of the hard coating layer, indicated the highest peak in theinclination section within the range of 25-35 degrees in the pole plotgraphs. Consequently, these cutting tools were unable to withstand thesevere mechanical and thermal shock during high-speed intermittentcutting, chipping occurred in the cutting edge, and the cutting toolsreached the end of their service life in a comparatively short period oftime.

As has been described above, the cutting tool of the present inventionis naturally capable of continuous and intermittent cutting of varioustypes of steel and cast iron under normal conditions, is extremelyresistant to mechanical and thermal shock, exhibits superior chippingresistance even during the most severe high-speed intermittent cuttingaccompanied the generation of a large amount of heat, and demonstratessuperior cutting performance over a long period of time. Thus, thecutting tool of the present invention is capable of satisfactorilyaccommodating increased performance of cutting devices, labor and energysavings in cutting processing, as well as reductions in costs.

1. A cutting tool provided with a tool base composed with tungstencarbide-based cemented carbide or titanium carbonitride-based Cermet,and a hard coating layer provided on the surface of the tool base;wherein the hard coating layer comprises: (a) at least one of a Ticompound and a Zr compound layer, which is a lower layer, comprising atleast one layer of a Ti carbide layer, Ti nitride layer, Ti carbonitridelayer, Ti oxicarbide layer, Ti oxicarbonitride layer, Zr carbide layer,Zr nitride layer, Zr carbonitride layer, Zr oxicarbide layer and Zroxicarbonitride layer formed by chemical vapor deposition, and having anoverall mean layer thickness of 0.5-20 μm, and (b) an aluminum oxidelayer having an α crystal structure in the state of being formed bychemical vapor deposition, which is an upper layer, comprising thehighest peak in the inclination section within a range of 0-10 degreesin the case of emitting an electron beam onto individual crystal grainshaving a hexagonal crystal lattice present within the measuring range ofthe surface polishing plane, measuring the inclination of the normal ofthe (0001) crystal plane of the crystal grains relative to the normal ofthe surface polishing plane using a field emission scanning electronmicroscope, dividing the measured inclinations within a range of 0-45degrees indicated by the individual crystal grains for each pitch of0.25 degrees, and preparing a pole plot graph by tabulating the measuredinclinations present in each section for each section, and having themean layer thickness is 1-30 μm.
 2. A cutting tool according to claim 1,wherein the hard coating layer has an aluminum oxide core thin layercontaining an aluminum oxide core between the lower layer and the upperlayer.
 3. A cutting tool according to claim 2, wherein the mean layerthickness of the aluminum oxide core thin layer is 20-200 nm.